The invention relates to a process for producing a tool insert used in a mold for injection molding a part fabricated of a synthetic material, a metal or a ceramic material and which includes an arrangement of microstructures formed on an outer surface of the part and have a predetermined depth. The invention also relates to an injection molding process for producing a part fabricated of a synthetic material, a metal or a ceramic material using the tool insert.
In order to ensure that parts which have been produced by means of injection molding can be removed from the tool after the injection molding process without the quality of the microstructures being impaired and in the case of a large number of microstructures without the removal force being excessive, it is necessary to provide the microstructures with inclined surfaces which enable the part to be removed from the molding tool, which surfaces are inclined, for example, at an angle of greater than two (2) degrees, wherein this angle is measured in the cross-section between a side wall of the microstructure and a plane perpendicular to the outer surface of the part and to the cross-sectional plane.
The following processes are known which render it possible to produce parts with single-stage microstructures:
(A) Wet etching glass
(B) Dry etching silicon
(C) LIGA
(D) UV-LIGA
(E) Laser Machining
(F) Micro erosion
(G) Microcutting (drilling, machining, turning)
However, all of these known microstructuring processes are encumbered with the following disadvantages:
It is only possible to achieve a limited maximum depth of the structure using process (A). Process (B) is difficult to manage. Process (C) is extremely time-consuming and costly. The inclined surface which enables the part to be removed from the molding tool cannot be produced using process (D) or it can only be produced at great expense. The processes (E), (F), (G) have not been sufficiently developed for use in industry and in addition can only be performed in sequence.
Broadly, one aspect of the present invention relates to a technique for making a portion of a mold having at least one microstructure by etching this microstructure on a wafer, attaching the wafer to a carrier substrate to form a master, depositing a material layer onto the master so that the deposited material extends over the microstructure, and then separating the material layer from the carrier substrate. Another broad aspect of the present invention relates to molding a part using a mold incorporating the mold portion that has been fabricated as described above.
A first aim of the invention is to provide a process for producing a microstructured tool insert of the type mentioned above which in the case of single-stage microstructures provides the inclined surfaces which enable the part to be removed from the molding tool to be produced at a relatively low cost.
According to a first aspect of the invention this first aim is achieved with a first process of the above-mentioned kind which comprises the following steps:
(a) photo-lithographically masking the front side of a first wafer with a first etching mask which corresponds to an arrangement of microstructures,
(b) micro-structuring the first wafer by means of plasma etching the front side of the first wafer to form an arrangement of microstructures which form cavities and whose depth extends over a part of the thickness of the first wafer,
(c) removing the first etching mask from the front side of the first wafer,
(d) bonding the front side of the first wafer to a carrier substrate to form a master,
(e) removing a layer of the first wafer to reveal the microstructures which have not been through-etched and to set the depth of the microstructures,
(f) applying an electrically conductive thin layer to the rear side of the first wafer and to the carrier substrate surfaces which can be accessed through the cavities mentioned,
(g) electrochemically depositing a metal layer on the rear side of the first wafer and in the cavities which are present therein and are formed by the microstructures,
(h) making planar the outer surface of the deposited metal layer, and
(i) separating the metal layer from the master, wherein the separated metal layer can be used as a tool insert for injection molding a part.
According to a second aspect of the invention the above-mentioned first aim is achieved with a second process of the above-mentioned kind which comprises the following steps:
(a) photo-lithographically masking the front side of a first wafer with a first etching mask which corresponds to an arrangement of microstructures,
(b) microstructuring the first wafer by means of plasma etching the front side of the first wafer to form an arrangement of microstructures, the depth of which extends over the entire thickness of the first wafer, so that the microstructures form cavities which have an orifice on the front side and on the rear side of the first wafer respectively,
(c) removing the first etching mask from the front side of the first wafer,
(d) bonding the front side of the first wafer to a carrier substrate to form a master,
(e) applying an electrically conductive thin layer to the rear side of the first wafer and to the carrier substrate surfaces which can be accessed through the cavities mentioned,
(f) electrochemically depositing a metal layer on the rear side of the first wafer and in the cavities which are present therein and are formed by the microstructures,
(g) making planar the outer surface of the deposited metal layer, and
(h) separating the metal layer from the master, wherein the separated metal layer can be used as a tool insert for injection molding a part.
In preferred embodiments of the above-mentioned first and second processes the first wafer is a silicon wafer.
In preferred embodiments of the above-mentioned first and second processes the carrier substrate is a glass wafer having a high sodium content, e.g. one fabricated from Pyrex(copyright) glass.
In other preferred embodiments of the above-mentioned first and second processes the carrier substrate is a silicon wafer.
In preferred embodiments of the above-mentioned first and second processes the deposited metal layer is a nickel layer.
In preferred embodiments of the above-mentioned first and second processes the microstructuring of the front side of the first wafer is performed by means of through-etching the first wafer with an undercut, so that the microstructures formed have a cross-section whose width increases with the distance to the front side of the first wafer.
Moreover, a second aim of the invention is to provide a process for injection molding a part which comprises an arrangement of microstructures which are formed on an outer surface of the part, have a predetermined depth and comprise inclined surfaces which enable the part to be removed from the molding tool, wherein a tool for injection molding is used which is formed from a first and a second tool half.
According to a third aspect of the invention the above-mentioned second aim is achieved with a third process of the above-mentioned kind which comprises the following steps:
(a) installing a first tool insert as a first tool half which serves to shape the arrangement of microstructures, wherein the first tool insert is produced according to according to a process of the above-mentioned kind,
(b) installing a second tool insert as a second tool half which is arranged opposite the first tool half,
(c) closing the tool formed from the first and second tool insert for injection molding,
(d) injecting a material melt into the cavity between the first and the second tool insert,
(f) cooling the injected material melt and
(g) ejecting from the molding tool for injection molding a part which is formed by the setting of the injected material melt and which comprises microstructures with inclined surfaces which enable the part to be removed from the molding tool.
The advantages achieved using the processes in accordance with the invention are as follows:
The process in accordance with the invention renders it possible in a convenient and inexpensive manner to produce inclined surfaces which enable the part to be removed from the molding tool and which are inclined at an angle greater than two (2) degrees. An important advantage of such inclined surfaces which enable the part to be removed from the molding tool is that they render it possible for the part to be removed from the molding tool without impairing the quality of the microstructures and for the forces required to remove the part from the molding tool to be low, even if the wafer comprises many microstructures.
The process in accordance with the invention obviates one disadvantage of dry etching silicon using the Bosch process, the fundamental undercutting of the structures.
The process in accordance with the invention has the additional advantage that uniformity of the depth of the etching is achieved through the thickness of the wafer and as a consequence is excellent, which is otherwise not the case when dry etching silicon in particular when the orifices are of different widths.